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Not a good thing Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 21 Jun 2001 11:27:07
In Reply to: ABS Brake fluid light 0n simultaneously only after stop & go, Joe D, Wed, 20 Jun 2001 21:27:06 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The ABS system uses pressurized brake fluid to drive the ABS system. This same pressure is used for brake boost. When the ABS light AND the Brake fluid light come on together, that means the ABS system pressure is below a safe point. Just the ABS light means other things, like a bad sensor.
The ABS pump pressurizes the system. As you drive and use the brakes, the pressure drops, and the pump runs to re-pressurize the system. Normally, the pump kicks in well before the minimum pressure that lights BOTH lights. It sounds like the pressure is dropping too far.
I can think of three things to cause this - First, the pump is tired, and can't keep up with the demand for pressure - basically, it's slow. This is bad because not only don't you have the pressure you need, the pump will be running all the time, and it will burn out.
Second, the pressure accumulator is leaking. Not leaking fluid into the engine compartment, but leaking fluid back into the brake fluid reservoir. Normally there is a slow leakage, but if that leakage gets big, the pump will spend a lot of time trying to keep up with it. Again, this can burn out a good pump.
Thirdly, a problem in the brake master cylinder. It uses the pressure to provide brake boost. If there is an internal leak in the MC, it will use a lot of pressure to provide boost. Again, the pump will run a lot, and may burn out.
You haven't noticed a problem (yet) because of a safety margin built into the system. Once those lights BOTH come on, you have enough pressure for between 5 and 10 normal stops before you lose brake boost. Since the pump is still running (because the lights go out), it's more than that. But if the pump stops (as it will do if it overheats from running too much), or you use up those stops before the pump can provide pressure, you'll lose brake boost.
Losing brake boost is very bad. The pedal will go hard, and although you will still be able to brake (by pressing VERY hard), your stopping distances will increase by 3 or 4 times. Think about that in stop and go traffic. You know how hard to press the brake, and when to press the brake, when the car in front of you stops. Most folks stop maybe a dozen or so feet from the car in front. You start braking a second or two earlier. Well, think about what would happen if one of those times the pedal was a rock. You'd have to react to that, and then press harder, and quickly. Even then, your 30 feet of stopping distance is not 90 or 120 feet. You WILL hit the car in front of you. How hard depends on how fast you're going. Not pretty.
You should get the system diagnosed as soon as possible. The bad news is that the ABS system is expensive. Make sure the mechanics actually troubleshoot the problem, not just say "It's the ABS, we'll need a new ABS computer, new ABS pump, and a new paint job and tires, that'll be $5000." It may just be a leaky accumulator or leaky Master Cylinder. Spend an extra $65 for an extra hour's worth of troubleshooting. It may save you a thousand at the back end. If they can't or won't troubleshoot, find a mechanic that will.
Good luck
, Thu, 21 Jun 2001 11:27:07 <-- Viewing This Message
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